In recent years, a motor for use in electric vehicles/hybrid electric vehicles (EV/HEV) uses a magnet having a reduced content of dysprosium (Dy) in order to reduce the cost of the magnet. The reduced content of Dy, however, may cause demagnetization at high temperature.
It is therefore important to grasp a magnet temperature, and it is necessary to estimate the magnet temperature and operate the motor so that the motor is prevented from being applied with an excessive demagnetizing field at high temperature. One example of such technology is to estimate the magnet temperature by detecting an induced voltage constant (see, for example, Patent Literature 1).